Objectives To explore the functional basis for the association between ankylosing spondylitis (AS) and single-nucleotide polymorphisms (SNPs) in the IL23R-IL12RB2 intergenic region.
Methods We performed conditional analysis on genetic association data and used epigenetic data on chromatin remodelling and transcription factor (TF) binding to identify the primary AS-associated IL23R-IL12RB2 intergenic SNP. Functional effects were tested in luciferase reporter assays in HEK293T cells and allele-specific TF binding was investigated by electrophoretic mobility gel shift assays. IL23R and IL12RB2 mRNA levels in CD4+ T cells were compared between cases homozygous for the AS-risk ‘A’ allele and the protective ‘G’ allele. The proportions of interleukin (IL)-17A+ and interferon (IFN)-γ+ CD4+ T-cells were measured by fluorescence-activated cell sorting and compared between these AS-risk and protective genotypes.
Results Conditional analysis identified rs11209032 as the probable causal SNP within a 1.14 kb putative enhancer between IL23R and IL12RB2. Reduced luciferase activity was seen for the risk allele (p<0.001) and reduced H3K4me1 methylation observed in CD4+ T-cells from ‘A/A’ homozygotes (p=0.02). The binding of nuclear extract to the risk allele was decreased ∼3.5-fold compared with the protective allele (p<0.001). The proportion of IFN-γ+ CD4+ T-cells was increased in ‘A/A’ homozygotes (p=0.004), but neither IL23R nor IL12RB2 mRNA was affected.
Conclusions The rs11209032 SNP downstream of IL23R forms part of an enhancer, allelic variation of which may influence Th1-cell numbers. Homozygosity for the risk ‘A’ allele is associated with more IFN-γ-secreting (Th1) cells. Further work is necessary to explain the mechanisms for these important observations.
- Ankylosing Spondylitis
- Gene Polymorphism
- T Cells
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Handling editor Tore K Kvien
Contributors BPW and CJC are joint senior authors. ARR, MV, LC, AR, AC, JCK, PB, CJC and BPW: conceived and designed the experiments. ARR, LC, MV, AR and CJC: performed the experiments. ARR, MV, LC, PB, CJC and BPW: analysed the data. ARR, MV, LC, AC, JCK, PB, CJC and BPW: wrote the manuscript.
Funding ARR was funded by Arthritis Research UK (grant 20402), MV by National Institute for Health Research (NIHR) Oxford comprehensive Biomedical Research Centre (immunity and inflammation theme A93081), LC by Arthritis Research UK (grant 20235) and AR by NIHR Oxford Comprehensive Biomedical Research Centre. JCK is funded by the European Research Council under the European Union's Seventh Framework Programme (FP7/2007–2013)/ERC Grant agreement no. 281824, Arthritis Research UK (grant 20773) and the NIHR Oxford Comprehensive Biomedical Research Centre. Additional funding was provided by Arthritis Research UK (grants 19356, 18797 and 20796), the NIHR Thames Valley collaborative research network, NIHR Oxford Musculoskeletal Biomedical Research Unit and National Ankylosing Spondylitis Society (UK).
Competing interests None declared.
Ethics approval Oxford C Research Ethics Committee 06/Q1606/139 and Oxford B Research Ethics Committee 07/Q1605/35.
Provenance and peer review Not commissioned; externally peer reviewed.
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